RPM display on dash and Forscan.

[sandancers]

I have noticed that when starting the vehicle (MK7 2014 E5 FWD 2.2l diesel) that while the engine is cranking over, trying to start that no rpm is shown on the dash rev counter or on the Forscan display which is recording various engine parameters. Indeed the Forscan display does not show most live data until the engine has started running after cranking.

Is this normal or abnormal ?

[gt_addict]

Normal for mine. I’m guessing either consistency in signal is required or potential battery voltage too low during cranking so the ecu/pcm doesn’t allow it to read until the voltage picks up. But thats just all guesswork.

[sandancers]

Just to close this off.

I was looking at the the rpm on forscan to see what the starter motor was doing at start up as it was a long crank to start after it had been standing for a day or two. What I found out was that when forscan was displaying live data and the engine rpm was below 150 forscan didn't show it, either because the program didn't like that figure or the pcm decided that the rpm figure was too low to be true.

Anyway, turned out that the starter motor was giving very low rpms at crank, so a new one has been fitted !

[tranmx2]

Indeed the Forscan display does not show most live data until the engine has started running after cranking.

Forscan live data can be populated before turning over/starting the engine. Press the roundal with the arrow in it - bottom left.

The RWD engine using Forscan shows the rpm the instant the engine fires. Key to start engine engage starter motor - count in my head 1 - and the rpm is up to 936 clutch dwn/in. Very close to instant.

A delay could be one of many things. Poor electrical connection, Insufficient fuel, fuel pressure. FRP before start is about 280 to 360 kPa. Engine started rpm 968 clutch pedal dwn/ in. FRP 23520 kPa. Clutch pedal up/off rpm 841 FRP 21520 kPa.

[sandancers]

Indeed the Forscan display does not show most live data until the engine has started running after cranking.

Forscan live data can be populated before turning over/starting the engine. Press the roundal with the arrow in it - bottom left.

The RWD engine using Forscan shows the rpm the instant the engine fires. Key to start engine engage starter motor - count in my head 1 - and the rpm is up to 936 clutch dwn/in. Very close to instant.

A delay could be one of many things. Poor electrical connection, Insufficient fuel, fuel pressure. FRP before start is about 280 to 360 kPa. Engine started rpm 968 clutch pedal dwn/ in. FRP 23520 kPa. Clutch pedal up/off rpm 841 FRP 21520 kPa.

I agree with all of the above. I had checked all the connections from the starter to the battery. Even a garage said "it's cranking speed is ok" then I saw an article which said that basically the MK7 will not spark up with a cranking rpm of below 250 rpm, because below that it cannot generate enough fuel pressure and the cylinders cannot give enough compression. Forscan would not show any rpm below 150 and even above that until sparking up the readings were "strange".

I took out the from new starter, 12 years old, but not had a massive amount of use because of being in a motorhome, maybe 50 starts per year, a Bosch unit, took it to bits, cleaned up the brushes and commutator and reinstalled it. No difference. So got an after market starter, put it in and the engine burst into life first spin !

So, this starter lived up to the reputation of going "lazy" and looking at the internals of the starter motor I think the common fault in them could be the return path for the main current within the starter motor ! I will have a closer look at that to prove my theory. But for now I am just happy it is a reliable starter again !

[metalworker0]

So starter was drawing excessive current for some reason .. look at the colour of the field windings , look at state of bearings .. the braided wire between starter and solenoid - often corroded., and the braided wires to each brush plus the stator windings .

looking up resistance test readings, what they should be on the different parts of a typical starter motor.

all the best.mark

[sandancers]

So starter was drawing excessive current for some reason .. look at the colour of the field windings , look at state of bearings .. the braided wire between starter and solenoid - often corroded., and the braided wires to each brush plus the stator windings .

looking up resistance test readings, what they should be on the different parts of a typical starter motor.

all the best.mark

I am not sure it was drawing excessive current. There is a 350A fuse in line with the starter. So I would say, as a totally rough guess, the starter takes @300A on a cold morning. And it could not have gone beyond 350A or the fuse would have popped.

I THINK that the return circuit from the commutator brushes to the main earth point on the starter had a larger resistance than it should have, which would in effect lower the current available to turn the starter under load.

And I THINK that if I am correct it would account for the many instances of "lazy starting" on the transit. It would seem to be quite common, which infers a common point of failure.